Confidence is indisputably a good thing. But over-confidence can spell trouble—especially when we’re learning. Research has shown over and over again that we are not very good judges of how effectively we’re learning new information, or how accurately we’ll remember it. This means we may stop the studying or training process prematurely, before new material is truly absorbed, and it means we may be in for an unpleasant surprise when we realize (at test or performance time) that we didn’t know that material as well as we assumed.

This overconfidence shows up in all kinds of settings: among debate teams taking part in a college tournament; among hunters quizzed about their knowledge of firearms just before the start of hunting season; and among medical residents evaluating their patient-interviewing skills, to cite a few examples collected by Cornell University psychologist David Dunning in a study published in the journal Current Directions in Psychological Science.